Every year millions of dollars worth of timber land, recreational facilities, homes and other natural resources are lost due to fire. Many of these fires take several days or even weeks to contain. Realizing that one way to stop the loss is to prevent the fires from occurring, great efforts are made and much time is spent in educating the public so that the fires will not occur. However, no matter how much care is taken, there is no way to stop forest fires from occurring.
Therefore, the next question is whether our present methods for fighting forest fires are adequate. Unfortunately, the answer seems to be “no.” When a fire breaks out in one of our forests, many crews of men are sent in to try and contain it, but they are not given effective tools in order to achieve their task. The men generally try to stop the fire by digging holes and grading roads and just plain hoping that the fire will not jump across the fireline. For reasons discussed below, fire retardant sprays and powders that are presently being used are generally not effective in stopping the travel of the fire.
The conditions necessary for the existence of fire are the presence of a combustible substance, a temperature high enough to cause or support combustion (called the kindling temperature), and the presence of enough oxygen (usually provided by the air) to enable combustion to continue. Therefore, fire fighting consists of removing one or more of these. It is known in the art to have water supplied to a fire to cool the fire below combustion temperatures. It is also known to involve chemicals other than water, especially useful for fires involving flammable liquids, particularly when water may be dangerous.
A variety of chemicals may be added to water to improve its ability to extinguish fires. For example, wetting agents added to water can reduce its surface tension. This makes the water more penetrating and facilitates the formation of small drops necessary for rapid heat absorption. Also, by adding foam-producing chemicals and liquids to water, a fire-blanketing foam is produced which is used to extinguish fires in combustible liquids, such as oil, petroleum, and tar, and for fighting fires at airports, refineries, and petroleum distribution facilities chemical additive can also expand the volume of foam, perhaps by 1000 times. This high-expansion foam-water solution is useful in fighting fires in basements and other difficult-to-reach areas because, the fire can be smothered quickly with relatively little water damage. It is also known to use chemicals, such as carbon dioxide, to displace needed oxygen from a fire. Carbon dioxide is used particularly for extinguishing fires because it does not burn and does not support ordinary combustion.
It is also known to have various equipment to deliver water or other chemicals to the fire. With the development of the internal-combustion engine early in the Twentieth Century, Fire Department pumpers became motorized. Because of problems in adapting geared rotary gasoline engines to pumps, the first gasoline-powered fire engines had two motors, one to drive the pump and the other to propel the vehicle. The pumps were originally of the piston or reciprocating type, but these were gradually replaced by rotary pumps and finally by centrifugal pumps, used by most modern pumpers. At the same time, the pumper acquired its main characteristics: a powerful pump that can supply water in a large range of volumes and pressures; several thousand feet of fire hose, with short lengths of large-diameter hose for attachment to hydrants; and a water tank for the initial attack on a fire while fire fighters connect the pump to hydrants, and for areas where no water supply is available. In rural areas, pumpers carry suction hose to draw water from rivers and ponds.
Various nozzles are capable of projecting solid, heavy streams of water, curtains of spray, or fog. Fire trucks carry a selection of nozzles, which are used according to the amount of heat that must be absorbed. Nozzles can apply water in the form of streams, spray, or fog at rates of flow between 57 liters (15 gal) to more than 380 liters (more than 100 gal) per minute. Straight streams of water have greater reach and penetration, but fog absorbs heat more quickly because the water droplets present a greater surface area and distribute the water more widely. Fog nozzles may be used to disperse vapors from flammable liquids, although foam is generally used to extinguish fires in flammable liquids.
Methods of fighting forest fires are necessarily different than fighting areas in developed areas, where access and water supply are generally less of a problem. Forest fires, often called wildland fires, are spread by the transfer of heat, in this case to grass, brush, shrubs, and trees.
Fire-fighting crews are trained and organized to handle fires covering large areas. They establish incident command posts, commissaries, and supply depots. Two-way radios are used to control operations, and airplanes are employed to drop supplies as well as chemicals. Helicopters serve as command posts and transport fire fighters and their equipment to areas that cannot be reached quickly on the ground. Some severe wildfires have required more than 10,000 fire fighters to be engaged at the same time.
Various forest fire fighting techniques are known in the art. However, the inventor has observed that these techniques require placing the fire fighting chemicals onto the fire from above. This may be difficult and may be inefficient. This is especially true if access is limited or difficult. In a forest fire, an aircraft may be used to drop chemicals onto the fire from above, but such chemicals must be designed to penetrate extremely hot conditions before reaching a location at which they can be effective. This may be inefficient. Furthermore, some of the chemicals may become dispersed in trees or other objects that are well above ground level thereby diminishing the amount of fire fighting chemical reaching the ground.
For example, aircraft such as the C-130 presently used for fire fighting by agencies such as the U.S. Forest Service are outfitted with liquid fire retardant dispersal systems including a liquid retardant reservoir, compressed air tanks, air compressor, discharge tube and nozzles, and related equipment all mounted on movable pallets. The systems are designed to perform multiple individual discharges each of several hundred gallons over a 4 to 5 second period, in a single flight, or to discharge the entire contents in a single burst. The systems are generally large and heavy, have power requirements that severely tax the available power supply aboard an aircraft, and potential electromagnetic interference (EMI) from the equipment that can be disruptive to the aircraft avionics.
Because it is frequently difficult to extinguish a forest fire by attacking it directly, the principal effort of forest fire fighters is often directed toward controlling its spread by creating a gap, or firebreak, across which fire cannot move. Firebreaks are made, and the fire crews attempt to stop the fire by several methods: trenching, direct attack with hose streams, the aforementioned aerial dispersing, spraying of fire-retarding chemicals, and controlled back-burning. As much as possible, advantage is taken of streams, open areas, and other natural obstacles when establishing a firebreak. Wide firebreaks may be dug with plows and bulldozers. The sides of the firebreaks are soaked with water or chemicals to slow the combustion process. Some parts of the fire may be allowed to burn themselves out. Fire-fighting crews must be alert to prevent outbreaks of fire on the unburned side of the firebreaks.
Furthermore, reflash, or re-ignition of an extinguished area may still occur if conditions are right. This presents a serious drawback in fighting the fire, and also presents a serious danger to crews. Chemicals applied from above may permit such conditions to occur.
It is clear that fire fighting, both in wilderness conditions and in developed areas, still lacks a capability of an immediate response safe to the fire fighter because of an inability to immediately deliver fire retarding chemicals to the fire in an efficient manner and in a manner that will prevent reflash of the fire.